Nowadays, for surgical applications increasingly assistance systems are used, comprising a holding arm, which is for example attachable to the slide rail of an operating table. For example, such a holding arm is used in shoulder operations for supporting the arm. It includes a plurality of rigid holding members which are movably coupled to each other by joints. Thus, the holding arm may be moved freely in all spatial directions and be fixed securely in the desired position.
The joints, which couple respectively two rigid holding members of the holding arm freely movable to each other, include a first joint body connected to one of the holding members and a second joint body connected to the other holding member. In order to fix the holding members in a desired arrangement with respect to each other, the two joint bodies have to be locked relative to each other.
A possibility for such a locking is described in DE 102 09 209 B4. Therein, one of the joint bodies includes a plurality of locking pins, while corresponding locking recesses are formed at the other joint body. An essential feature of said locking mechanism is that the number of locking recesses is higher than the number of locking pins. In a specific embodiment, thirteen locking recesses and twelve locking pins are provided. In the locked state, respectively one of the locking pins engages completely in one of the locking recesses, while the locking pins immediately adjacent to said pin are only partially inserted in their associated locking recesses. Thus, the clearance-free locking of the joint is assisted.
In order to allow this kind of engaging of the locking pins in the locking recesses, the locking pins respectively include an engagement part having the shape of a truncated cone. The locking recesses are correspondingly tapered in a truncated cone-shaped manner. This ensures that in the locked state of the joint, said locking pin being completely inserted in the corresponding locking recess contacts the locking recess with its engagement part over the entire surface. In contrast, the engagement parts of said locking pins being only partially inserted in the corresponding locking recesses only have line contact or only a very slight surface contact with the corresponding locking recesses.
In practical use, it turned out that a holding arm using a locking of the above-explained type is subject to certain restrictions with respect to high load applications. Thus, the holding arm has to be operated by means of a handle, which is coupled to an unlocking mechanism acting on the joints, in order to unlock the joints. The higher the load, the more manual force has to be exerted.